The invention relates to the field of imaging systems, and particularly relates to imaging systems in which a continuous web of media is fed through an imaging apparatus.
Imaging systems that feed recording media through an imaging apparatus may include a movable optical carriage that displaces a beam of light from an imaging source, such as a laser. The carriage moves in a direction transverse to the direction of movement of the web in a slow scan to expose a supply of recording media to the light beam. The carriage itself typically includes a beam deflector assembly such as a deflector mirror and a spin motor for rotating the deflector mirror. Such a carriage for use in an imaging system including an internal imaging drum for supporting the recording media, is disclosed for example in U.S. Pat. No. 5,598,739, the disclosure of which is hereby incorporated reference.
As shown in FIG. 1, in a conventional imaging system 10 including an imaging drum 12, a web of image recording media 14 travels from a supply cassette roll 16 around the inner support surface 18 of the drum 12 to a take up cassette roll 20. The media generally has sufficient inherent stiffness that it maintains the cylindrical shape of the inner surface 18 of the drum 12 when coupled to cassette rolls 16 and 20. A movable carriage 22 may be used to position a beam of laser light 24 on desired portions of the recording surface 26 of the media 14. The imaging system 10 is typically coupled to a computer controlled image processor (not shown). Although it is important that as few components as possible contact the recording surface 26 of the media 14, the media 14 may be driven by nip rollers 28 and 30. The desired direction of movement of the web through the drum is shown generally at A.
The media 14 may also be indexed to register separate images by punching holes in the media at specific places such as by punches 32. The punch holes are later used to precisely register the media on printing equipment. Precise alignment of the media on printing equipment is critical for a number of reasons, including the fact that multiple passes may be undertaken to print a multi-color image of high resolution. The media, however, must be aligned on a printing device, such as a drum, either in the orientation dictated by the punch holes, or new punch holes must be created along at least one of the sides of the media. The process of providing the additional punch holes in recorded media requires additional steps that must be undertaken with care and precision, and introduces added costs and potential for error into the overall printing process.
It has been discovered that if punches such as those disclosed above are employed along a side edge of the web in the direction of travel of the web, then several problems persist that reduce the quality and/or consistency of recorded media. In particular, if the opening in such a punch is too large, then the media may jump (and possibly shift) as the punch element is removed from the media, and if the punch opening is too small, then the media may bind as it enters the punch (and even as it travels through the punch). Movement of even a small amount may cause misalignment due to the stringent alignment requirements of such imaging systems.
The use of punches having variable size openings that are adapted to provide a large size opening when the media is entering the punch and thereafter a smaller size opening, may overcome certain of the above difficulties. However, the use of a variable size opening punch also introduces the potential of alignment error as portions of the punch move relative one another. Again, movement of even a small amount may cause misalignment. Moreover, the use of punches having variable size openings increases mechanical complexities and risks damaging expensive recording media if mechanical failure occurs with respect to the punch.
There is a need, therefore, for an imaging system that permits alignment holes for aligning images to be provided along at least one side of recording media in the direction of travel of the web. There is further a need for such an imaging system that provides sufficient alignment quality and consistency.